[Feature] Encapsulate interface logic (#1320)

* Provide a utility function for aligning text

* Replace lvim banner with one using only ASCII chars

* Use strings.format instead of .. operator

* Center text in the popup based on its dimentions

* Minor improvements

* Provide a popup factory function

* Add function documentation

* Improve text alignment

* Print marker only if provider list is not empty

* Format client capabilities as list

* Pretty format lsp client capabilities

* Add a metatable to popup.lua

* Improve rendering when no lsp is available

* Take cmdheight into acount when computing popup size and pos

Co-authored-by: kylo252 <59826753+kylo252@users.noreply.github.com>

lua/interface/text.lua

@@ -0,0 +1,79 @@
+local M = {}
+
+local function max_len_line(lines)
+  local max_len = 0
+
+  for _, line in ipairs(lines) do
+    local line_len = line:len()
+    if line_len > max_len then
+      max_len = line_len
+    end
+  end
+
+  return max_len
+end
+
+--- Center align lines relatively to the parent container
+-- @param container The container where lines will be displayed
+-- @param lines The text to align
+-- @param alignment The alignment value, range: [0-1]
+function M.align(container, lines, alignment)
+  local max_len = max_len_line(lines)
+  local indent_amount = math.ceil(math.max(container.width - max_len, 0) * alignment)
+  return M.shift_left(lines, indent_amount)
+end
+
+--- Shift lines by a given amount
+-- @params lines The lines the shift
+-- @param amount The amount of spaces to add
+function M.shift_left(lines, amount)
+  local output = {}
+  local padding = string.rep(" ", amount)
+
+  for _, line in ipairs(lines) do
+    table.insert(output, padding .. line)
+  end
+
+  return output
+end
+
+--- Pretty format tables
+-- @param entries The table to format
+-- @param col_count The number of column to span the table on
+-- @param col_sep The separator between each colummn, default: " "
+function M.format_table(entries, col_count, col_sep)
+  col_sep = col_sep or " "
+
+  local col_rows = math.ceil(vim.tbl_count(entries) / col_count)
+  local cols = {}
+  local count = 0
+
+  for i, entry in ipairs(entries) do
+    if ((i - 1) % col_rows) == 0 then
+      table.insert(cols, {})
+      count = count + 1
+    end
+    table.insert(cols[count], entry)
+  end
+
+  local col_max_len = {}
+  for _, col in ipairs(cols) do
+    table.insert(col_max_len, max_len_line(col))
+  end
+
+  local output = {}
+  for i, col in ipairs(cols) do
+    for j, entry in ipairs(col) do
+      if not output[j] then
+        output[j] = entry
+      else
+        local padding = string.rep(" ", col_max_len[i - 1] - cols[i - 1][j]:len())
+        output[j] = output[j] .. padding .. col_sep .. entry
+      end
+    end
+  end
+
+  return output
+end
+
+return M